The Michael Reaction of Silyl Enol Ethers with α,β-Unsaturated Eetones and Acetals in the Presence of Titanium Tetraalkoxide and Titanium Tetrachloride

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Abstract
Silyl enol ethers react with α,β-unsaturated ketones and esters in the presence of TiCl4 or in the coexistence of TiCl4 and Ti(Oi-Pr)4 to give 1,5-dicarbonyl compounds in good yields. The reactions of acetals derived from α,β-unsaturated ketones with silyl enol ethers in the coexistence of TiCl4 and Ti(Oi-Pr)4, followed by successive addition of 1,2-ethanedithiol, give the Michael products, δ-keto ethylene thioacetal, in good yields. The reaction of silyl enol ethers with acetals derived from α,β-unsaturated aldehydes also gives the Michael products when Ti(OCEt3)4 is employed instead of Ti(Oi-Pr)4 in the above experiment and is successfully applied to the simple synthesis of dihydro rose oxide.